Objectives: 1) To test the validity of a pathophysiologic classification of diarrhea as either secretory or osmotic on the basis of stool volume, electrolyte and osmolality determinations during fed and fasting conditions. 2) To determine whether a common mechanism(s) exists for secretory diarrhea, possibly through alterations of mucosal cyclic adenosine monophosphate, adenosine triphosphate: adenosine diphosphate ratio or enzyme activity in the glycolytic pathway. 3) To determine the specific etiologic agent(s) inducing the secretory diarrhea in patients.